1. Field of the Invention
The present invention relates to methods of cementing subterranean zones, cement compositions and oil suspensions of powder useful in cement compositions.
2. Description of the Prior Art
Hydraulic cement compositions are utilized in cementing subterranean zones penetrated by well bores. For example, hydraulic cement compositions are used in primary well cementing operations whereby strings of pipe such as casings and liners are cemented in well bores. In performing primary cementing, a cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
In primary well cementing and in other subterranean cementing operations, large quantities of crystalline and amorphous silica powder are often included in the cement compositions utilized. Crystalline silica powder is included in cement compositions to prevent cement compressive strength retrogression, i.e., the loss of compressive strength and increased permeability. Amorphous silica powder is also commonly utilized as a light weight filler and to increase the cement compressive strength by reacting with lime to form calcium-silicate-hydrate gel.
Heretofore, the crystalline and amorphous silica powder utilized have been combined with cement in mechanical blending equipment. As a result of the handling and mixing of the silica with the cement, significant amounts of the silica powder and dust are released into the atmosphere. Personnel in the area are often exposed to the powder and dust which can cause silicosis, a chronic disease of the lungs caused by the inhalation of silica powder and dust.
Thus, there is a need for eliminating the silica powder and dust produced during the handling and blending of silica with cement.